The present invention relates to a device for measuring and correcting a parallelism error in a nuclear fuel rod, more particularly a parallelism error in the end provided with the upper plug.
A nuclear fuel assembly is made up of a plurality of nuclear fuel rods arranged parallel to each other such that the assembly has a substantially square transverse section.
Each fuel rod comprises a fuel clad, which is a very long tube with a small diameter, covered at its lower end and in which the cylindrical nuclear fuel pellets with a circular section are stacked. When the required number of pellets has been introduced into the fuel clad, its open end is covered by a plug, called the upper plug. This assembly formed by the fuel clad, the lower and upper plugs and the pellets constitutes the fuel rod.
The assembly comprises a lower end receiving the end of each fuel rod provided with a lower plug and an upper end receiving the end of each fuel rod provided with the upper plug. The lower end and the upper end are provided with housings individually receiving each rod end. The upper and lower ends are connected by rigid rods so as to form a rigid frame.
In order to be able to guarantee a good connection between the fuel rod, more particularly its end provided with the upper plug, and the upper cap, the parallelism of the upper plug end must be sufficient.
However, a parallelism error may appear at the end of the upper plug when the upper plug is welded on the lower plug welded tube, or LPWT, which corresponds to the fuel clad provided with the lower plug. Such an error can also appear due to an accidental deformation of the end of the upper plug during the handling of the fuel rods. Other causes can be at the root of this parallelism error.
Document JP10 123283 describes a device for measuring the parallelism error of a fuel rod end comprising a probe, the fuel rod being made to rotate.
This document also describes a device for measuring a parallelism error comprising at least two linear probe probes orthogonal to the axis of the fuel rod, to measure the axis of the upper plug, the use of at least two probes making it possible to avoid making the fuel rod rotate. This measurement makes it possible to measure the gap between the axis of the upper plug and that of the fuel rod.
These measuring devices do not make it possible to correct the parallelism error.
Moreover, correcting the error must be very controlled to avoid creating another parallelism error, by overcorrecting the first error.
It is therefore one aim of the present invention to offer a device making it possible both to measure a parallelism error and correct it, reliably.